1. Field of the Invention
The present invention relates to an adapter for clamps, particularly for welding plastic pipes.
2. Description of the Prior Art
Plastic pipings for conveying fluids are made by butt-welding pieces of pipes, tees, bends, etc. Among the various technologies known to perform the welding, one of the most widely used is polyfusion of the head portion.
Special welding machines are used to perform this type of welding.
The specific welding machines will not be described herein, it may be known however that the pipes, tees, bends, etc. that compose the piping, in order to be welded together, must have the same diameter and thickness and must be axially mutually aligned during welding.
Particularly, in the case of welding of pipes for fluids under pressure and in any case for pipes that have a substantial thickness, the welding machines have a supporting frame on which four aligned clamps are mounted and lock the head portions of the pipes to be welded in pairs. Two mutually opposite hydraulic pusher cylinders are associated with the clamps and allow the movement of the clamps so as to bring into contact the heads of the pipes to be welded.
The clamps are generally sized so as to clamp a specific maximum diameter and are provided with adapters for reducing the diameter.
Each clamp is constituted by two jaws that are articulated at one end: one jaw is fixed to the frame while the other one is movable. A mechanical or hydraulic closure device is provided at the end that lies opposite the articulation end.
Those jaws form two concave mutually opposite portions that are substantially semicircular and form the seat for locking the corresponding pipe to be welded.
The adapters of the clamp consist of bodies that have a substantially semicircular contour and in practice form a C shape and are arranged and fixed within the complementarily shaped concave portion of a corresponding jaw.
Conventionally the adapters are made of cast aluminum.
The concave surface of the adapters which clamps the pipe generally has ridges provided transversely with respect to the directrix of the pipe in order to avoid any slippage.
The choice to make the adapters by cast aluminum arises from the need to achieve a final weight which is not excessive and is therefore practical for on-site ease of handling of the adapter combined with good structural strength.
In addition to the cost of aluminum as a raw material, there is a cost due to the work for finishing the adapters. The cost of this work is more or less onerous depending on the precisions of the mold used for casting.
For example, if one uses a sand mold, it is necessary to perform substantial reworking of the cast part in order to obtain a final product which has the intended dimensional and shape tolerances.
If, instead a pressure die-casting method is used, reworking is minimal, with a saving in finishing costs with respect to sand casting; however, die casting has the disadvantage of a considerable investment in terms of molds, that are much more expensive, because of the greater dimensional precision, than sand molds. If it is necessary to provide many types of reduction unit, the investment in molds becomes very onerous.
In recent years, the cost of aluminum as a raw material has been increasing constantly.
The overall costs for manufacturing aluminum adapters are therefore increasingly important also as a percentage on the total cost of a complete welding machine.